Q: In order to lose only fat what kind of cardio should we do and how many times a week?Whats the difference of simple cardio and Hiit?When should we use hiit and how many times a week?

A: The two most important thing for successful fat loss are a good diet and a good weight-training program! Cardio or HIIT are only secondary. So please read my fat-loss article and make sure your diet and weight training are up to par. Once that's taken care of you can decide what kind of cardio to do...

'Traditional' cardio requires you to stay at constant or nearly constant pace for a period of time -- 15 minutes or 30 minutes or longer. During that period you will burn some fat and you will also burn some muscle. How much of each depends on a large number of factors, but the most important thing in general when doing traditional cardio is to make sure you do not lose weight too quickly! Loss of 1 pound per week is a good pace for most people. Traditional cardio will eat up more of your muscle when you're losing weight too fast. This form of cardio stresses your aerobic energy system and usually has little or no impact on your metabolism (meaning that the fat burned during the exercise is all the fat that you'll lose).

HIIT (High Intensity Interval Training) looks like regular cardio, but really stresses your body a lot more like weight training does. HIIT consists of alternating 30-second periods of all-out sprinting and walking. It can be done using any sort of activity -- from running to biking to swimming, though running is the most common. For example, a typical 4-minute HIIT session would look like this (after a warm-up): 30 seconds of all-out sprint, 30 seconds of relaxed walk, 30 seconds of all-out sprint, 30 second walk, 30 second sprint, 30 second walk, 30 second sprint, 30 second walk. That's it! You would do HIIT 2-3 times per week slowly increasing session length from 4-5 minute sessions in the first week to eventually 12-15 minute sessions in later weeks. As I said, HIIT is a lot more like weight training than cardio as far as your body is concerned and it has similar effect: it does not burn much fat during the activity itself, but it raises your overall metabolism so your body burns fat AFTER the activity as it recovers and repairs the muscles.

If you already do full-body weight training, you can choose either HIIT or traditional cardio or mix and match them as you like. If you don't do any weight training, I would strongly recommend that you definitely do HIIT as well as traditional cardio.